I'm planning on switching to T-Mobile. Though my contract doesn't end until January, how much would it cost to leave?

Depends on the type of phone you purchased. Advanced phones(smartphones and maybe some 3G MM) ETFs are $350 minus $10 for each month of service completed. Non-advanced are $175 minus $5 for each month completed.

i'm still trying to fight with VZ over their data plans. you cannot get a new smartphone without paying $30/month.

This is not true. Currently, Verizon is offering a $15/150MB/month data plan. You may have to watch your data usage to make sure that you do not go over the 150MB, though. If you go over, you will be charged another $15 for the next 150MB and so on.

Actually, the ETF's are not inflated. If you sign a 2yr contract on say a DROID X and end up paying a net $200, that means Verizon is SUBSIDIZING YOUR PURCHASE to the tune of $400. If you BREAK your contract, Verizon recoups PART OF THAT SUBSIDY to the tune of $350 less $10 for every month you have completed of your contract.

You do not have to have ANY ETF's with Verizon if you do not want to have an ETF. JUST PAY THE NON SUBSIDIZED PRICE OF THE PHONE. You will then not have to sign a contract and can leave at any time without paying an ETF.

Even if you DO sign a contract and leave immediately and pay the ETF, you are already making out by paying a net price for the phone that is $50 less then then non-subsidized price that Verizon sells it for.